Infections caused by the herpes virus are among the oldest known to man. Recurrent herpes simplex labialis has been reported to affect almost one-half of the population of the United States, and 25 per cent of those affected have frequent and/or severe recurrences. Genital herpes, though not officially recognized as a disease until 1966, is currently an epidemic venereal disease. About five million Americans suffer from this problem, with an estimated one-half million individuals having become infected in 1981 alone. Although many forms of therapy have been tested, none has proven profoundly beneficial in decreasing the severity and frequency of the clinical manifestations. Systemic regimens adequate to suppress skin symptomology often result in adverse systemic effects and still may not overcome the inaccessibility to the drug of the target tissue. "Drug delivery" remains the singularly most limiting factor to the effective treatment of herpes. Preliminary studies showing that interferon can be delivered across intact skin when incorporated in liposomes suggest a means of treating certain skin infections. The goal of these studies is to assess the possibility of treating virus-infected epithelial cells with liposomally entrapped interferon delivered by the transdermal route. Specifically, we wish to isolate and elucidate the factors associated with the liposomal entrapment of biologically active interferon and with its subsequent delivery through intact skin to tissue infected by virus. Since interferon's biological activity is long-lasting when in liposomes, liposomes also appear to offer a practical as well as an effective means of delivery of interferon to lesion sites. Furthermore, a systematic analysis of the parameters involved may provide a rational hypothesis and guidance for future research on the delivery of liposomal interferon by other routes of administration for the treatment of other disease states.